The present invention relates to saw guards and, more particularly, to saw guards for use with multipurpose woodworking tools having a table saw mode of operation.
Some multipurpose woodworking tools are of the type having a frame, a motor-driven headstock slidably mounted on the frame, and a plurality of accessories which are also mounted on the frame and are powered by the headstock. A common accessory with such multipurpose woodworking tools is the saw table which includes a table top having a central blade slot and a pivot attachment to a pair of legs. The legs are joined by a tie bar and adjustably mounted for vertical movement on a carriage slidably attached to the frame of the woodworking tool. A circular saw blade is mounted on a quill spindle which extends from the headstock, and the headstock and saw table are positioned such that the circular saw blade extends upwardly through the table slot. Standard table sawing operations may be performed on such a device.
An example of such a multipurpose woodworking tool is shown and described in the Edgemond, Jr. et al. U.S. Pat. No. 2,927,612. That multipurpose woodworking tool includes a quill spindle which is part of a quill assembly that can be advanced and retracted relative to the headstock so that the multipurpose tool can be modified to perform horizontal boring and vertical drill press operations. However, when modified to function as a table saw, the quill assembly can be adjusted to position the circular saw blade within the slot of the saw table.
In order to cover the exposed portions of the circular saw blade which protrude above and below the saw tables of such mulitpurpose woodworking tools, removable saw guards have been developed. These saw guards perform the dual function of shielding the circular saw blade and containing the sawdust and other debris generated during a table sawing operation. One type of saw guard commonly used includes a two-piece lower saw guard which covers the portion of the saw blade extending beneath the saw table, and an upper shield, preferably made of a transparent plastic material, which encloses the portion of the saw blade extending above the saw table.
The lower saw guard consists of a rear portion that attaches to the quill of the headstock and includes a spring-loaded slide that is urged upwardly against the underside of the saw table, and thereby provides a continuous enclosure regardless of the relative elevation of the saw table to the headstock. This portion of the lower saw guard encloses the rear and periphery of a saw blade attached to the quill. The front of the saw blade is enclosed by a tie bar shield which attaches to the tie bar of the saw table and includes an upper edge which extends toward the table slot. The rear portion of the lower saw guard includes a vacuum port shaped to receive the hose of a shop vacuum so that sawdust generated during operation and collecting within the lower saw guard is removed.
The upper shield pivotally attaches to a spreader or splitter, which is plate-shaped and adjustably positioned to lie in a common plane with the saw blade. The splitter attaches to a bracket attached to the side of the tie bar, and therefore moves relative to the saw blade as the table is raised or lowered.
Although this type of saw guard adequately shields a circular saw blade, there are some drawbacks with such a design. For exmaple, since the splitter is attached to the tie bar, it is necessary to position the quill of the headstock so that the saw blade is coplanar with the splitter when the multipurpose tool is modified to function as a table saw. Should the saw table be moved relative to the quill spindle for any reason, or the quill spindle moved relative to the saw table, it would be necessary to realign the blade with the splitter before using the table saw again.
Another disadvantage is that the pocket formed by the tie bar shield and rear portion of the lower saw guard is not adjustable so that the efficiency of the dust removal system varies with the type of tool mounted on the quill. That is, a saw guard designed for maximum efficiency when used in combination with a circular saw blade may not provide the same level of efficiency when a dado blade, or molder is used. Since the vacuum port of such a saw guard is connected to the rear portion of the lower saw guard, the ability of a vacuum cleaner to remove dust generated by a sanding wheel is reduced because the port is located behind the work surface of the sanding wheel. Furthermore, this lack of adjustability prevents some tools from being used with that type of saw guard. The sanding disk is one example.
The dust removable capability of such saw guards is also reduced by the bosses which support the spring-loaded slide. These bosses protrude into the pocket and create turbulence within the pocket during operation which reduces the efficiency of the saw guard in directing dust to the vacuum port.
A disadvantage with those saw guards that include splitter mounted on the saw table is that the saw guard is fixed relative to the elevation of the table and therefore is raised and lowered relative to the saw blade as the table height is adjusted. When the saw table is elevated, a large gap is formed between the splitter and saw blade which may tend to reduce the effectiveness of the splitter in preventing binding of the blade with the kerf and in preventing kickbacks.
Another common component of prior art saw guard assemblies is the anti-kickback device which prevents the spinning saw blade from throwing a workpiece back toward the user. One form of anti-kickback device includes a pair of pawls pivotally attached at their upper ends to the splitter, and having teeth formed in their lower ends. The pawls are spring biased to pivot downwardly, and ideally the pawl is angled rearwardly when it engages a workpiece so that a maximum number of teeth contact a workpiece passing beneath it. In such a position, a workpiece is permitted to slide relative to the pawls in a downstream or feeding direction, but will be held by the pawls against the table if urged in an upstream direction by the saw blade.
A disadvantage with this type of anti-kickback device is that its effectiveness is dependent upon its angular orientation relative to the workpiece; maximum effectiveness is achieved in a relatively narrow range of angles in which a maximum number of pawl teeth contact the workpiece. Since this angular orientation is determined by the distance from the pivot connection of the pawl with the splitter to the upper surface of the workpiece, the effectiveness of the pawl is dependent upon the thickness of the workpiece and the height of the splitter above the table.
Accordingly, there is a need for a saw guard which is designed to be used in combination with a multipurpose woodworking tool that is sufficiently adjustable to function efficiently when used with a variety of rotary tools, such as circular saw blades, sanding wheels, dado blades and the like. Furthermore, there is a need for a saw guard which can remain fixed relative to a rotary tool even though the quill spindle and saw table are adjusted relative to the multipurpose tool frame. There is also a need for a saw guard in which the splitter remains coplanar and closely adjacent to the saw blade regardless of the relative elevation of the saw table, and includes an antikickback device that is highly effective regardless of the workpiece thickness or table orientation.